Overview
Expected yearly worldwide demand for road rehabilitation works concerns about 1.7 million km of roads. This creates a large need for natural resources used, but on the other hand bears significant potential for reuse of existing pavement materials. As asphalt pavements are in theory 100% recyclable, suitable techniques should be continuously developed and supported. Cold recycling can be seen as a technology where several benefits and added-value are linked - natural resources can be reduced, energy consumption decreased, road infrastructure protected from excessive construction-related transport and rehabilitation works can be shortened. The potential for multiple recycling is a significant benefit - the only question is the activation of the old binder. If proper mix design is applied and suitable binders used including activating the bituminous binder in reclaimed material new structure will lead to increased bearing capacity and improved pavement durability. Despite this, no more than 35 % of reclaimed asphalt is reused in cold recycling.
This project focuses mainly on harmonising mix design of cold-recycled bitumen stabilised materials following the existing scientific and engineering experience and approaches. The key objective is to develop and recommend comprehensive mix design and characterisation by studying compaction methods, curing procedures and performance tests. The output should be applicable to all variants of cold-recycled mixtures containing bituminous binders or combination with other binders or alternative fines. Aspects considerable for defining durability of cold-recycled mixtures will be evaluated and specified as well.
Existing practice focuses only on water immersion and stiffness. Both characteristics are not a standard part in all mix designs known in Europe. Nevertheless to vindicate and promote cold recycling as an equivalent solution for hot mix asphalt the durability must be predictable. For this reason the project focuses on assessing stiffness, fatigue behaviour, resistance to cracking and on long-term moisture effects. Different test procedures will be evaluated and most suitable approach recommended including proposed threshold limits. This will make performance-based mix design possible. Further gained results will be used for formulating preferable inclusion of cold-recycled mixture in existing pavement design manuals. It is primarily not expected to modify the mechanistic calculation of pavement design, more important seems to be the definition of typical structures where cold-recycled bitumen stabilised materials are used for base or binder courses and critical parameters are defined. This should allow to road administrators and designer to use cold-recycled mixtures as a standard component of a pavement structure.
Multiple recycling should present one of the key advantages of cold recycling techniques. The activation of reclaimed asphalt, impact of material ageing and range of applicability (for cold recycled mixtures and for the partial substitute of aggregates in hot mix asphalts) will be specified and the most suitable practice recommended. The final part of the project focuses on environmental stability/compatibility which becomes an integral part of building materials' use and modern civil engineering. Leaching of cold-recycled mixtures will be specified with recommendations for threshold limits. At the same time some hazardous or problematic materials in existing pavements will be assessed in relation to their immobilisation and most suitable reuse by cold recycling (tar, asbestos, crumb-rubber modified asphalt). Part of this environmental assessment will be devoted to technically correct assessment of cold-recycled mixtures with respect to their carbon footprint. It is believed, that in the near future, such energy equivalent will be considered in decision about most appropriate technical solutions in pavement construction or rehabilitation and energy savings achievable by recycling should be considered as a benefit.
The project bundles the capabilities of science, public interests and industrial knowledge to overcome the described problem and to offer an appropriate solution.
Funding
Results
The original intention of CoRePaSol project was to seek for suitable tool applicable for calculating eco-balance between the existing professional applications which can be found on the market. Preferably it was expected to create a suitable synergy with the tool developed within CEREAL project. This idea nevertheless so far failed since the Carbon Road Map software tool developed by CEREAL is still not available for public use. Additionally it was found that cold recycling techniques could not be simply included. Especially, if the intention was to show effects of different combinations of machinery used for cold recycling technologies. In the second step it was analysed if there could be easier solution to include effectively cold recycling techniques to British asPECT software tool. Even this was finally not decided as a most suitable way and finally the project team started to structure available technical data in a way to create their own simple calculation tool. This Excel based application is able to compare different technical solutions of performing cold recycling. It is linked to a detailed database of machinery data. Special attention has been paid to describe as good as possible the daily snapshot of a regular cold recycling procedure. Material data, mainly of bitumen and cement, are taken from existing life-cycle inventories.
Finally, the principles of the Excel based calculation tool developed within CoRePaSol are summarised. To make the benefit and application of the tool clearer to the reader, this includes calculations for hypothetical construction site which can be rehabilitated by different ways of cold recycling. In several tables the input data as well as receiving outputs of the calculations are shown and described to demonstrate the overall idea of this calculation tool. It is even shown how impact of different generations of a construction machine (recycler) can be interpreted with respect to the impact such recycler has to the environment. Gained results and conclusions have to be always put in relation to economic values to demonstrate the possible effects. It is mainly important to describe the practical use for decision on suitable recycling technique and have the opportunity to compare different approaches from environmental point of view (public sector perspective) as well as to compare the influence of selected generations of machinery and its contribution to emission release (more private sector perspective). The most important conclusion is nevertheless the ration of material-based and machinery-based emissions, which could additionally demonstrate the benefit of cold recycling.